The overarching goal of this project was to improve our ability to predict coastline evolution in response to changes in sediment delivery by rivers and sea level rise.  We tested the hypothesis that sediment amount and grain size control a delta’s form and internal deposits.  The sub-goals were to predict delta form, facies distributions, sandbody geometries and connectivity, distribution of mud drapes, and through-going surfaces important for hydrocarbon and groundwater exploitation.  In particular, we conjectured that, all other factors equal, a sandy delta would have more active distributaries, a less rugose shoreline, less topographic variation, and less variability in its offshore bathymetry than a delta constructed by a mud-dominated sediment load; and its stratigraphy would have a steeper delta front, a greater percentage of channel facies, and less rugose sand bodies than a highly cohesive delta.

We predicted the variables defined above using Delft3D, a physics-based computer model simulating 3D fluid flow and sediment transport and then compared the predictions to cores, serial aerial photography, bathymetry, outcrop measurements, and ground penetrating radar datasets from two modern deltas representing end-members of the modeling results--the Wax Lake delta, LA and the Goose River delta, Labrador--and one ancient delta--the Cretaceous Ferron Last Chance Delta of Utah.

These model results are consistent with data collected from the Goose River Delta, a coarse-grained fan delta prograding into Goose Bay, Labrador, Canada.  The Goose River flows into Goose Bay at the western end of Lake Melville, Labrador.  Goose River delta sediments consist of arkosic, heavy-mineral-rich sand (D50 = 225 microns) with only moderate amounts of silt and clay, placing this delta at the coarser-grained, non-cohesive end of the spectrum.  The delta started to form approx. 7000 years ago as the Laurentide ice sheet retreated and post-glacial rebound created a relative base level fall of approximately 4 mm/yr.  The current tidal range in Goose Bay averages 0.5 m, and the average wave height is negligible.  Results from our two field seasons show that the delta planform consists of three moribund lobes at elevations of ~15, ~ 5, and ~ 2 m and a presently active delta at sea level.  Aerial photography from 1951 to 2012 show there has been surprisingly little progradation despite active channel change at the six-month timescale and an assumed base level fall of 244 mm during that period. A topographic section along a dipline consists of three treads and two clinoform risers.  The bottomset tread is a virtually featureless fjord bottom at ~35 m from which a first clinoform rises to a second tread at ~-15 m. The second tread is a sandy platform onto which an upper clinoform downlaps. This upper sandy clinoform ranges in dip from 9 to 17 dg and passes into the topset at an elevation of ~ -1 m.  The topset consists of braid-like trapezoidal unit bars that in GPR show little evidence of wave, alongshore current, or ice reworking, even though they are submerged at higher high tides.  The planform, bar geometries and facies, and clinoform dips and dip-directions are remarkably consistent with model predictions from Delft3d.

Although sea level is general rising around the World, there are northern latitude regions where the retreat of the last continental glaciers is creating a relative sea level fall.  We also documented and quantified the morphologic and stratigraphic character of deltas subject to falling sea level.  The numerical simulations predicted that the number of active distributaries decreases with an increase in the rate of base level fall and that the shoreline becomes increasingly irregular, whereas mean clinoform dips near the rollover and clinoform concavity sh...

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